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Abstract

We show that our recently reported microwave photonic jet technique for detection of deeply subwavelength pits in a metal substrate can be extended to optical wavelengths for purposes of high-density data storage. Three-dimensional finite-difference time-domain computational solutions of Maxwell’s equations are used to optimize the photonic nanojet and pit configuration to account for the Drude dispersion of an aluminum substrate in the spectral range near λ=400 nm. Our results show that nanojet-illuminated pits having lateral dimensions of only 50 nm×80 nm yield a contrast ratio 27 dB greater than previously reported using a lens system for pits of similar area. Such pits are much smaller than BluRay™ features. The high detection contrast afforded by the photonic nanojet could potentially yield significant increases in data density and throughput relative to current commercial optical data-storage systems while retaining the basic geometry of the storage medium.

FDTD-computed far-field no-pit/pit power ratio as a function of the nanojet wavelength and the pit depth for a single rectangular 50 nm×80 nm (lateral cross-section) pit in the complete optical data-storage model of Fig. 1.

FDTD-computed far-field no-pit/pit power ratio vs. pit depth for a 50 nm×80 nm lateral cross-section pit at the fixed wavelength λ=393.9 nm. The monotonic nature of this characteristic over a wide range of power ratios and ~90 nm of pit-depth variation suggests a pit-depth coding scheme wherein multiple data levels are encoded at the location of a single pit according to its depth.

FDTD-computed far-field no-pits/pits power ratio vs. pit-to-pit separation for a pair of 50 nm×80 nm rectangular pits, each having the optimum pit depth of 30 nm. The wavelength is fixed at λ=393.9 nm. The two pits are assumed to be positioned7lengthwise along the y-direction centered within the nanojet’s footprint shown in Fig. 2(c). The monotonic nature of this characteristic over a wide range of power ratios and ~300 nm of pit-to-pit separation suggests a scheme wherein multiple data levels are encoded at the location of a single pit-pair within the nanojet footprint according to the pit-to-pit separation distance.